The concept of proteolytic activation of prothrombin to thrombin by "intrinsic" and "extrinsic prothrombinas", trypsin, thrombin, and citrate has been receiving increasing attention. From information now available there is considerable similarity in activity, inhibition, and the amino acid sequence of the serine active site between thrombin, trypsin and chymotrypsin. The chemical mechanism of chymotrypsinogen- chymotrypsin and trypsinogen-trypsin conversion is well established, however, little is known of the chemical mechanisms in the conversion of prothrombin to thrombin. The objectives of this research project are (1) to define the peptides split in human prothrombin during its conversion to thrombin, by using bovine prothrombin as a model (2) to establish the order of their release; (3) to determine their location in the prothrombin molecule; (4) to develop a new clinical method for purification of human prothrombin from small amounts of human plasma; (5) to use column or paper "Peptides maps" standards of activation of normal human prothrombin for comparison to those derived from abnormal human prothrombins and also to those derived from the activation of normal human prothrombin by abnormal human plasma. The action of intrinsic and extrinsic systems and the products produced by prothrombin degradation will be tested on the chemical and kinetic activation of prothrombin. The experimental results of these new approaches will provide more insight and a better understanding of the mechanism of blood coagulation and new sensitive analytical procedure for defining abnormal human plasma and abnormal human prothrombin and prothrombin split products in plasma.